Method for producing inorganic oxide fibers



March 19, 1963 Q E. F. MAYER ETAL 3,082,055

METHOD FOR PRODUCING INORGANIC OXIDE FIBERS Filed Aug. 10, 1960 EDWARD F. MAYER VIRGIL E.STRAUGHAN KZZIJM y ATTORNEY INVENTORS I United States Patent 3,082,055 METHOD FOR PRODUCING INORGANIC OXIDE FIBERS Edward F. Mayer, Novelty, and Virgil E. Straughan,

Euclid, Ohio, assignors to Horizons Incorporated,

Cleveland, Ohio, a corporation of New Jersey Filed Aug. 10, 1960, Ser. No. 48,767 1 Claim. (Cl. 1854) This invention relates to the production of solid fibers of inorganic oxide compounds from suitable liquid com ggsitions, and particularly a method for producing such ers.

In earlier filed copending applications assigned to the same assignee as the present application, namely United States patent applications Serial No. 777,193, filed December l, 1958; Serial No. 829,220, filed July 24, 1959; and Serial No. 11,121, filed February 26, 1960, processes have been described for the production of fibers of zirconia, alumina, silica and other similar inorganic oxides, or combinations of such oxides, by the removal of liquid from sols and solutions of specified controlled compositions. More specifically, application Serial No. 777,193 describes and claims the formation of inorganic filaments of specific aspect ratios by a method which comprises spreading a thin film of a lyophobic sol of an inorganic oxide material on a smooth solid surface of a material to which the lyophobic material does not adhere when it is dried thereon and drying the film to remove the liquid therefrom, the lyophobic sol preferably being of an inorganic oxide material selected from the group consisting of oxygen-containing compoundsof silicon, zirconium, aluminum, chromium, thorium and mixtures thereof with one another and with oxides of boron. Application Serial No. 829,220 describes the preparation of filaments from the oxides of metals which are less basic than the oxides of the alkali and alkaline earth metals,

and specifically from metal salts of organic acids of the metals including aluminum, the rare earths, zirconium, hafnium, thorium, niobium, tantalum, chromium, manganese, iron, cobalt and nickel. Application Serial No. 11,121 describes the preparation of fibers consisting of a major proportion of an inorganic oxide other than silica and a minor amount of silica from a thin layer of a solution containing a metal salt of a carboxylic acid whose dissociation constant is greater than 1.5 il0 a metal salt of a strong mineral acid; and a silica sol; by exposing the thin layer of solution to infrared while it is on an infrared absorbing support, the major portion of the fiber being an oxide of an element selected from the same group of metals as those indicated to be useful in Serial No. 829,220.

In order to render the processes disclosed therein economically practical, a continuous processing technique would manifestly offer many advantages.

One object of the present invention is to provide a method whereby fibers having specific properties and dimensions may be produced.

Another object of the invention is to provide a method wherein the above object is accomplished continuously.

Still another object is to provide means for producing fibers characterized by uniformity of dimensions and uniformity of properties.

These and other objects are realized by the method hereinafter described, one form of which is schematically illustrated in the single FIGURE of the drawings accompanying this description.

As shown in the drawing, a preferred apparatus comprises a drum supported in any suitable manner permitting rotation about a central axis 12. Preferably the drum is formed of a metal cylinder 8 and is surfaced with a thin layer 10 of resistant material such as a fired assasss Patented Mar. 19, 1963 enamel coating, or an electrolytic plate. The drum is operatively connected to a variable speed gear train adapted to drive it at any desired speed, e.g. through driven rollers 11 which make physical contact only with the end portions of the drum.

At the lowermost point of its travel the drum physically contacts an applicator roller 14. Applicator roller 14 is mounted for rotational movement independently of the drum. Suitable means are provided for adjusting the pressure between roller 14 and the drum and thereby controlling the amount of liquid applied by applicator roller 14 to the surface of the drum. A portion of applicator roller 14 bathes in a bath 16 of fibering liquid contained in a tank '18. Tank 18 is provided with a cooling jacket 19 for maintaining the temperature of bath 16 at any desired level and for preventing overheating of the fibering liquid. Fibering liquid is fed to tank 1 8 from a supply reservoir 20, past a metering valve 22, at a rate slightly in excess of the rate at which liquid is carried away on the surface 10 of the drum. Tank 18 has an overflow outlet 24 to maintain the level of bath 16 at a height determined by the overflow outlet 24. Liquid pasing from outlet 24 is discharged through a cooling means 26 and is collected in a tank 28 from which it is returned by a pump (not shown) to reservoir 20.

As the drum rotates, a controlled amount of fibering liquid drawn from bath 16 by applicator roll 14 is dragged along on the drum surface upwardly past a source of heat, schematically shown as a first bank of radiant heaters 30 spaced between about 4 and 6 inches from the drum surface and a second bank of heaters 32 which provide the heat for additional drying found necessary to permit the fibers to pull away readily from the drum surface.

The dried, loose fibers are gathered either by hand or by means of a tube 40 having a thin slit 42 extending along one edge. Tube 40 is connected to a source of vac uum so that the loose fibers are sucked in through the slot. 40

means for detaching any remaining fiber deposit from the A spring loaded knife edge scraper 44 serves as a surface of the drum, although many of the fibers fall away from the drum surface freely, when dried properly.

additional scrapers of flushing or washing by liquids has not been found to be necessary. The fresh liquid applied by roller appears to dissolve any traces of residual solids present on the drum.

One specific apparatus constructed and operated in accordance with the present invention comprised the following:

The drum was a 24 inch diameter, 16 inch wide enamell-ed steel drum. I

The drum was supported on four rubber-tired wheels, two of which were driven by a variable speed drive.

Applicator roller 14 was a soft polyurethane roller 2 inches in diameter and 10 inches long.

Applicator roller '14 was driven in the opposite direction to the drum.

Tube 40 was positioned between A and inch above the point where knife edge 44 met the drum.

From the preceding description of the apparatus, the practice of the method is believed to be readily apparent. For purposes of illustration, one specific fibering composition is described but it is to be understood that the method is applicable to the production of fibers from any suitable fibering composition such as those described in the aforementioned pending patent applications.

A fibering liquid was prepared by mixing together zirconyl acetate, zirconyl chloride, calcium chloride and sufficient water to provide a composition containing 92.9% by weight of zirconyl acetate, 5.38% Zirconyl chloride and 1.72% CaCl in addition to water.

The resulting composition was vacuum dried to reduce its volume about 4%40% by removal of water. To the resulting composition a small amount of carboxyrnethylcellulose was added to yield a viscosity of about 8 to 14 centipoises. High viscosity solutions yield large fibers low viscosity solutions give fine fibers resulting in lower production rate.

Rotation of the drum was begun at a speed of .7 rpm. and the application of fibering liquid to the drum surface was initiated. The heating means Was energized and fibers began to form shortly thereafter.

The physical dimensions and the properties of the fibers formed as the drum revolves, and indeed the very process of fiber formation have all been found to be significantly affected by the amount of fibering liquid which is dragged out of pool 16 and into the nip between roller 14 and drum 8. This amount, which is controllably variable, is determined by the following:

-(1) The speed of the drum 8.

(2) The speed of applicator roller 14.

(3) The relative physical dimensions of drum 8 and applicator 14, the clearance between them and their physical characteristics.

(4) The physical properties of the fibering liquid (surface tension, viscosity, gelation, etc.).

The drum and applicator are readily controlled by the operator, based on experience and visible evidence.

To control the fiber forming process it has been found necessary (1) to maintain the temperature of the fibering liquid within narrow limits, and (2) to prevent or avoid the application of gelled liquid to the drum surfaces. Both of these conditions have been found to be satisfied by recirculation of the fibering liquid in the apparatus described above. In operation, the drum temperature has been found to have increased to about 183 F. at the point of fiber removal due to heat imparted to the drum by heaters 33 and 32 when processing the liquid described above. If the drum were immersed directly in bath 16, the heat which the drum would impart to bath would be sufficient to gel the composition and would render it useless for the intended purpose. To overcome this, it is necessary to diminish the temperature of liquid in the bath 16, or to diminish the temperature of the drum surface before application of the fibering liquid to the drum. Since the residual heat in the drum surface assists in the fibering process, the first alternative is preferable.

As shown in the drawing, the preferred apparatu includes means for recirculating the fibering liquid to control the temperature of the liquid and to effect resolution of any gel formed and to thereby prevent the application of gel to the drum surface. The rate at which liquid recirculates is readily controlled by outlet 24 or by metering valve 22. In addition, an applicator roller is used to meter the amount of liquid applied to the drum.

With a drum speed of about 5 linear feet per minute and with about 3200 watts supplied by heaters 30, drying of freshly applied fibering liquid begins almost immediately due to the residual heat in drum 8, and proceeds as the drum covered with liquid moves past the heaters. Furthermore, by controlling the rate of recirculation and the cooling capacity, the temperature of the fibering composition described above may be maintained at about 23 C. to 24 C., in bath 16', an optimum value for the specific system described. As a result of having properly controlled the several variables as described above, fibers form readily from the fibering liquid and are collected by the collection means 40, 42.

Typical fibers produced in accordance with the invention described above had the following dimensions: length, As to /2; width, 25 to 400 and thickness, 0.511. 10 4a.

The properties of the dried fibers may be further improved for certain purposes, by firing them at temperatures up to 1700 C. and even higher as disclosed in the above noted copending applications.

While a specific preferred embodiment of the invention has been described in accordance with the patent statutes, it will be evident that the method and apparatus described may be applied to the formation of fibers from other fibering liquid compositions.

In an application for patent Serial No. 48,551, filed of even date herewith, we have more fully described and claimed the control of viscosity of the fibering liquid.

Having now described our invention in accordance with the patent statutes, we claim:

In a continuous method of producing filaments composed of inorganic oxide of an element selected from the group consisting of silicon, zirconium, aluminum, chromium, thorium and mixtures thereof With one another, wherein the filaments are produced as a result of the application of heat and removal of water from a thin film of an aqueous liquid composition supported on a smooth solid surface to which the filaments do not adhere; the improvement which comprises: increasing the production of fibers with dimensions within a desired range by maintaining the aqueous liquid composition supplied as said thin film at a temperature sufficiently low that the liquid composition does not gel when applied to the heated surface of a rotary drum, by circulating said liquid through a cooling means and thence to a pool of said liquid from which a thin fihn of said cooled liquid is applied to the surface of said drum, and by withdrawing a portion of the liquid from said pool and recirculating said withdrawn liquid through said cooling means and then returning the resulting cooled liquid to said pool; continuously spreading said liquid as a thin film on the surface of a rotary drum, and thereafter applying heat to said thin film of liquid on said drum and then recovering the filaments formed as a result of the removal of water from said thin film'and the consequent formation of filaments from said film.

References Cited in the file of this patent UNITED STATES PATENTS 1,142,829 Maywald June 15, 1915 1,178,027 Scharwath Apr. 4, 1916 2,266,636 Houser Dec. 16, 1941 2,556,217 Rivoche et a1 June 12, 1951 2,644,195 Bennes et al. July 7, 1953 2,681,294 Beguin June 15, 1954 2,915,475 Bugosh Dec. 1, 1959 

